A common means for attaching spiral staircase treads to a central column includes hollow cylindrical collars that slide over and surround the central column, wherein each tread is attached to a respective collar such as via weldment. Each collar stacks on top of the lower collars so that the height of the collar determines the vertical spacing between the treads.
In other cases, each tread will attach to a curved mounting plate with an inner radius of curvature about a vertical axis that is equal to the radius of curvature of the column's outer diameter, and the mounting plates attach to the column via bolts. However, repeated use of the staircase causes vibrations that can cause the bolts to loosen.